Writing Drivers for NetBSD - of index.html

1 PREFACE 4
1 Preface
This document is intended to teach the basics of Unix-Kernelprogramming to a
beginning Programmer with basic C knowledge. As an example, a device driver
for a floppy drive under NetBSD was chosen, as the hardware and necessary documentation
was available but the driver itself missing. NetBSD was chosen as the
target operating system, as it lends itself perfectly as a teaching example due to its
clearly structured source code and well defined interfaces.
Unfortunately, there is hardly any specific documentation on Unix-
Kernelprogramming under NetBSD apart from references to the functions in section
9 of the NetBSD manual pages. These manual pages are however missing
an introduction, a document that clarifies the connection between the various
functions. This document attempts to provide such an introduction, to act as the
necessary glue between the individual parts. Therefore, I will reference external
documents, particularly section 9 of the NetBSD manual pages in many places.
This document is mainly based on the experiences I made when I wrote the driver
rf(4) 1 for the UnixBus / QBus RX211 8” floppy controller.
8” floppy? Those things existed? Yes. Those were the first floppies, built at
the end of the 60s / beginning of the 70s. UniBus / QBus? Whatsdat? That’s the
most common bus found in VAXen 2 . The VAX was the machine of the late 70s
up until the beginning of the 90s. Then it was obsoleted by the Alpha architecture.
BSD Unix has a long and glorious history on the VAX. [McK 99] But why am I
writing a driver today for such antiquated technology? In the end, it doesn’t really
matter if I explain the necessary steps using the latest 1GBit/s Ethernetcard for
a PCIX Bus or anything else. The underlying principles are the same. Besides,
the hardware used in this example is relatively simplistic, so that we can see the
essential aspects instead of being hindered by PeeCee idiocrasy.
The following chapter gives a short overview of the autoconf(9) concept in
NetBSD. Some details have been omitted, and I refer to the according manual
pages to avoid duplication of information.
The third chapter documents the implementation of the autoconf(9) interface
of rf(4).
The fourth and last chapter covers the actual driver, i.e. the functionality of
the driver carrying the data from and to the physical device.
In the appendix, you will find the complete source code of the driver as well
1 RX01/02 Floppy
2 plural for VAX